In the design of electronic systems which include frame mounted modules often consisting of printed circuit boards and the like it has become customary, practical, and preferable to concentrate the hardware for providing various major system functions in separate ones of the printed circuit boards. By this means simplified modular maintenance and overall improved system operation are economically achieved. Therefore in new systems there is a trend toward lesser duplication of individual modules, or stated differently there is a greater proliferation of module types.
For example electronic telecommunication switching systems typically require circuit modules for functions of line interface, trunk interface, network switching, signalling, call control and power supply. More recently newer functions of digital line interface, voice messaging, text messaging, data practical conversion, data language translation and mass storage have been suggested as being value added services which are particularly desirable in systems of the electronic private branch exchange (EPBX) type. The various circuit modules have quite different connection requirement, however as such systems vary widely in function and size it has been found convenient to provide at least two physical circuit locations which will accept modules of one general type or another such that the EPBX is economically tailorable to a customer's requirements. Hence it is typical practice to segregate those modules concerned with line and trunk interface functions to a shelf with network and line and trunk interconnect facilities and to segregate the remaining modules with network and controller interface requirements into another shelf in the EPBX.
Very recently it has become practical to achieve massive reductions in module size or conversely to achieve improvements in traffic and feature capability through the practical application of extra large integrated circuit technology. Economies achieved would be further enchanced if the practice of segregation could be discarded or made less rigid.